1. Field of the Invention
The present invention relates to a liquid crystal display device and particularly to a drive circuit for a white light-emitting diode constituting the light source of a backlight.
2. Description of the Related Art
A liquid crystal display device generally includes a liquid crystal display panel and a backlight irradiating the liquid crystal display panel with light. A liquid crystal display device used as a display part of a mobile device such as a mobile phone includes a white light-emitting diode as the light source of a backlight.
As an LED drive circuit for the white light-emitting diode, an LED drive circuit having a dimming control function with a dimming control signal PWM has been known.
FIG. 5 is a circuit diagram showing a circuit configuration of a conventional LED drive circuit, showing an example of the LED drive circuit having the dimming control function with the dimming control signal PWM.
The LED drive circuit shown in FIG. 5 includes a booster circuit 1, a white light-emitting diode column 5 formed of one or two or more white light-emitting diodes LED connected in series with one another, and a resistance element 2 setting a current flowing in the white light-emitting diode column 5.
A voltage generated across the resistance element 2 is input to the booster circuit 1 as a control voltage VCONT. Based on the output voltage of an operational amplifier OP which outputs the difference voltage between the control voltage VCONT and a reference voltage Vref, an internal control circuit 10 boosts an input voltage Vin to generate an output voltage Vout so that the control voltage VCONT becomes a constant voltage.
The output voltage Vout of the booster circuit 1 is applied to the white light-emitting diode column 5. In this case, since the control voltage VCONT applied to the resistance element 2 is controlled so as to become constant, the current flowing to the white light-emitting diode column 5 is set based on the control voltage VCONT applied to the resistance element 2 and the resistance value of the resistance element 2.
In the LED circuit, the boosting operation of the booster circuit 1 is ON/OFF controlled with the dimming control signal PWM, whereby the turning on and off of the white light-emitting diode column 5 is controlled.